Bostrycapulus, common name the "spiny slipper snails", is a genus of sea snails, marine gastropod mollusks in the family Calyptraeidae, the slipper snails, cup-and-saucer snails and hat snails. Before 2005, the snails in this genus were all thought to belong to one species, which was known as Crepidula aculeata, the spiny slipper snail.However, morphological and DNA sequence data show that the spiny slipper snails are a monophyletic group that is more closely related to Crepipatella than it is to Crepidula.